With respect to an airbag installed as a safety device for an automobile, in an airbag prepared by a hollow weave, two pieces of base fabric are joined by a weave to form an inflatable inflation part, and in order to provide airtightness, a coating material such as a silicone resin is applied onto the outer surface.
However, in a case of trying to obtain favorable internal pressure maintaining performance by such a method, it is required to increase the applying amount of a silicone resin, the thickness and the weight are increased, and the storability may be deteriorated in some cases. In addition, it is known that in the outer peripheral joining part positioned on the outer periphery of an inflation part, weave shifting (yarn slippage) of the base fabric is easily generated at the time of inflation, and in a hollow weave airbag by silicone coating, the gas leakage generated from the yarn slippage point greatly affects the internal pressure maintaining performance of the airbag.
Accordingly, as one of the methods for improving the internal pressure maintaining performance, a hollow weave airbag by lamination has been studied. According to the lamination, reduction of the internal pressure maintaining performance due to yarn slippage of an outer peripheral joining part is improved. However, by suppressing the gas leakage from the yarn slippage in the outer peripheral joining part, gas leakage from a cut face is generated, and there has been a case where sufficient internal pressure maintaining performance is not obtained.
There have been no sufficient studies to cope with the gas leakage from a cut face of such a laminated hollow weave airbag.
For example, in Patent Literature 1, a technique in which in a hollow weave airbag that has a closed part including two or more weaves and adjacent to the bag part, and the closed part is constituted of a first weave from the bag part side, and a second weave adjacent to the opposite bag part side, by making the first weave looser than the second weave, the stress at the time of deployment does not concentrate, and an opening is suppressed has been disclosed. However, in this literature, gas leakage from a cut face has not been considered, and it cannot be said that it is sufficient as a technique for suppressing gas leakage particularly from a laminated hollow weave airbag.
Further, in Patent Literature 2, a technique in which in a weave of a boundary part between a non-inflating part and an inflating part as a bag body, by having a weave in which upper fabric constituent yarns repeat sinking and floating once or more under lower fabric constituent yarns, and the lower fabric constituent yarns repeat sinking and floating once or more on the upper fabric constituent yarns, the upper fabric constituent yarns and the lower fabric constituent yarns both constituting multiple fabric, the yarn slippage in the boundary part is reduced has been disclosed. Although it is considered that it is effective for suppressing the gas leakage due to yarn slippage by having high weave density in a joining part, as in Patent Literature 1, gas leakage from a cut face has not been considered.
As described above, in these literatures, effective countermeasures against the gas leakage from a cut face forming the outer periphery of an airbag that is an object of the present invention have not been suggested.